Method and system for data synchronization in passive optical networks

ABSTRACT

A system and method for data synchronization in Passive Optical Networks are disclosed. According to an embodiment, the present invention provides a method for providing upstream data synchronization in an optical communication network. The method includes sending data from an Optical Network Unit. The data includes a first data frame, which includes a header sequence, a synchronization segment, and a data segment. The synchronization segment includes 66 bits, which includes a first number of bits having nonzero values and a second number of bits having a value of zero. The first number is different from the second number. The method further includes receiving at least the first data frame by an Optical Line Terminal. The method also includes processing the first data frame. The method additionally includes selecting a first segment of the first data frame, the first segment including 66 bits.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/577,446, filed on Oct. 12, 2009, which is a continuation ofInternational Application No. PCT/CN2008/071395, filed on Jun. 20, 2008.The International Application claims priority International PatentApplication No. PCT/CN2007/071056, filed on Nov. 13, 2007 andPCT/CN2007/071253, filed on Dec. 17, 2007. The afore-mentioned patentapplications are hereby incorporated by reference in their entireties.

FIELD OF THE INVENTION

The present invention relates in general to telecommunicationtechniques, more particularly, to a method and system for providing datasynchronization in Passive Optical Networks (PONs).

BACKGROUND OF THE INVENTION

To improve readability and clarity of this application, acronyms areused. A listed of acronyms is provided below:

PON Passive Optical Network

VoIP Voice over Internet Protocol

HDTV High Definition Television

OLT Optical Line Terminal

ONU Optical Network Unit

ODN Optical Distribution Network

TDM Time Division Multiplexing

TDMA Time Division Multiple Access

ID Identification

SOD Start of Data

BD Burst Delimiter

HFP High Frequency Pattern

AGC Automatic Gain Control

CDR Clock and Data Recovery

FSC False Synchronization Candidates

HD Hamming Distance

HDC Hamming Distance Calculation

SDM Synchronization Decision Module

MSB Most Significant Bit

LSB Least Significant Bit

PON is one of the most promising access network technologies. This typeof network provides many benefits, including low maintenance cost, highbandwidth, low implementation cost, etc. PON can be an ideal platformfor multi-play applications such as VoIP, data transmission, HDTV, etc.

Typically, PON is implemented as a point-to-multipoint medium based on atree topology including an Optical Line Terminal (OLT), some OpticalNetwork Units (ONUs) and an Optical Distribution Network (ODN) withsplitters/couplers. One of the most attractive features of a PON is thatthe PON does not need any active component in the ODN.

Usually, PON system employs a point-to-multipoint access protocol sothat all subscribed ONUs can share an OLT over an optical fiber. Forexample, the Time Division Multiplexing (TDM) broadcast for downstreamtransmission and Time Division Multiple Access (TDMA) for upstreamtransmission is widely used in current PON systems.

As merely an example, FIG. 1 illustrates a downstream transmissionprocess in a PON system. The OLT broadcasts signals to all subscribedONUs in the downstream transmission, the destination ONU will extractits belonging packets according to the destination identification (ID)of a packet and discard all other packets as in FIG. 1. For example,ONU-1 extracts the packet with its destination ID and sends to itscorresponding end user; ONU-2 sends packet-2 to its end user, and so on.

As merely an example, FIG. 2 illustrates an upstream transmissionprocess in a PON system. The ONU transmits its signal in upstreamchannel of a PON system in a burst mode, which is different from theconventional point to point continuous mode transmission. ONU will firstset up a communication link with the OLT, thereafter OLT will allocatedifferent time slots to different ONUs in a TDMA fashion so that theirsignals will not overlap with each other when they reach the coupler inthe ODN. As shown in FIG. 2, the ONU-1 only transmit its signal in itstime slot (i.e., No. 1) and ONU-2 transmits its signal in its time slot(i.e., No. 2), and so on.

FIG. 3 is a simplified diagram illustrating a frame structure forupstream data. A high frequency pattern (HFP) “0x 55 55 . . . ” (0xmeans hexadecimal numbers and its binary form is 01010101 01010101 . . .) is a special preamble sequence used by the OLT for Automatic GainControl (AGC) and Clock and Data Recovery (CDR). The HFP is followed bya 66 bits long Start of Data <SOD> delimiter, or it is called BurstDelimiter (BD). The SOD is used to delineate the boundary of the dataframe. The length of SOD delimiter is compatible with the 66-bit dataframe structure. The section labeled FEC protected “ . . . ” could beone or several IDLE blocks that are used by OLT for de-scramblerre-synchronization and codeword delineation. Data are appended afterthis (these) IDLE block(s).

The SOD is useful in data synchronization. FIG. 4 is a simplifieddiagram illustrating the correlation between SOD and FalseSynchronization Candidates (FSC). After the OLT detects incoming signaland synchronizes the signal with its clock reference, the OLT will sendthe received signal to the Boundary Detector. A SOD Correlator isembedded within the Boundary Detector module to test the correlationbetween the SOD delimiter and the received signal. The SOD Correlatorwill calculate the Hamming distance (HD) between the SOD delimiter andthe received 66 bits data to determine the validation of burstsynchronization, which is the same as delineate the boundary of the dataframe. A false locking synchronization will output a truncated dataframe to its higher layer, this may degrade the system performance.Therefore, the employed SOD delimiter should provide a false lockingprobability as low as possible. The SOD delimiter should be designed tominimize the correlation between the SOD delimiter and the FSC, in otherwords, maximize the HD between the SOD delimiter and the FSC.

As can be seen from the above description that, various conventionaltechniques are available for data synchronization in optical networks.Unfortunately, these techniques are often inadequate for variousreasons.

Therefore, improved system and method for data synchronization aredesired.

SUMMARY OF THE INVENTION

The present invention relates in general to telecommunicationtechniques. More particularly, the invention provides a method andsystem for providing data synchronization in PONs. In a specificembodiment, the present invention provides a technique for upstreamsynchronization using optimized SOD sequences and the hardwareimplementation thereof. Merely by way of example, the invention isdescribed as it applies to PONs, but it should be recognized that theinvention has a broader range of applicability. For example, theinvention can be applied to any communication systems uses specifiedsequences for data synchronization.

According to an embodiment, the present invention provides a method forproviding upstream data synchronization in an optical communicationnetwork. The method includes sending data from an ONU. The data includesa first data frame, which includes a header sequence, a synchronizationsegment, and a data segment. The synchronization segment includes 66bits, which includes a first number of bits having nonzero values and asecond number of bits having a value of zero. The first number isdifferent from the second number. The method further includes receivingat least the first data frame by an OLT. The method also includesprocessing the first data frame. The method additionally includesselecting a first segment of the first data frame, the first segmentincluding 66 bits. The method further includes comparing the firstsegment with a synchronization delimiter. Moreover, the method includesdetermining a Hamming distance based on the first segment. The methodadditionally includes determining a boundary of the data frame.

According to another embodiment, the present invention provides a PONsystem includes a number of ONUs. The optical network includes atransmitter. Each ONU is configured to send data using the transmitterin a TDMA fashion. The data include a first data frame, which includes aheader sequence, a synchronization segment, and a data segment. Thesynchronization segment including 66 bits, which includes a first numberof bits having nonzero values and a second number of bits having a valueof zero. The first number is different from the second number. Thesystem also includes an OLT. The OLT includes a receiver that isconfigured to receive at least the first data frame. The OLT alsoincludes a shifter register for storing the first data frame. The OLTincludes a logic circuit for comparing the first segment with asynchronization delimiter. The OLT additionally includes a Hammingdistance module for determining a Hamming distance based on the firstsegment. The OLT includes a Synchronization Decision Module (SDM)determining a boundary of the first data frame.

It is to be appreciated that embodiments of the present inventionprovides various advantages over conventional techniques. Among otherthings, by using optimized synchronization delimiter sequences and thehardware thereof, the synchronization process is optimized both forspeed and reliability. In addition, embodiments of the present inventioncan be easily implemented using and/or in conjunction with conventionalsystems with minimal modification. There are other benefits as well,which are described below.

Depending upon embodiment, one or more of these benefits may beachieved. These benefits and various additional objects, features andadvantages of the present invention can be fully appreciated withreference to the detailed description and accompanying drawings thatfollow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a downstream transmission process in a PON system.

FIG. 2 illustrates an upstream transmission process in a PON system.

FIG. 3 is a simplified diagram illustrating a frame structure forupstream data.

FIG. 4 is a simplified diagram illustrating the correlation between SODdelimiter and false synchronization candidates.

FIG. 5 is a simplified diagram illustrating upstream transmission froman ONU to an OLT in a PON system.

FIG. 6 is a simplified diagram illustrating SOD delimiter being used indata frame.

FIG. 7 is a simplified diagram illustrating an upstream data framestructure of a 10G EPON system according to an embodiment of the presentinvention.

FIG. 8A is a simplified diagram illustrating a synchronization circuitof the SOD Correlator according to an embodiment of the presentinvention.

FIG. 8B is a simplified diagram illustrating hard logic for providingSOD delimiter logic according to an embodiment of the present invention.

FIG. 9 is a graph illustrating the comparison of false lockingprobability between existing techniques and an embodiment of the presentinvention.

FIG. 10 is a simplified diagram illustrating an upstream data framestructure of a 10G EPON system according to an embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The present invention relates in general to telecommunicationtechniques. More particularly, the invention provides a method andsystem for providing data synchronization in PONs. In a specificembodiment, the present invention provides a technique for upstreamsynchronization using optimized SOD sequences and the hardwareimplementation thereof. Merely by way of example, the invention isdescribed as it applies to PONs, but it should be recognized that theinvention has a broader range of applicability. For example, theinvention can be applied to any communication systems uses specifiedsequences for data synchronization.

As discuss above, conventional data synchronization techniques are ofteninadequate for various reasons, which are explained in detail below.

FIG. 5 is a simplified diagram illustrating upstream transmission froman ONU to an OLT in a PON system. The FEC codewords are composed to forman upstream data frame in the Frame Formator.

The HFP and the SOD delimiter sequence will then be appended to thebeginning of the data frame as shown in FIG. 3, respectively. Thecurrently employed SOD is a 66 bits binary sequence. For example, thebinary sequence is the following, {00 01010100 10101110 1111100111011010 01111000 00111101 11000010 01000110} and its hexadecimalrepresentation is {0x 0 54 AE F9 DA 78 3D C2 46}. It should be notedthat every hexadecimal number represent 4 binary bits, except the firsthexadecimal number or the leading number, which represents 2 binarybits. The minimum distance of the current employed SOD delimiter and theFSC is 31. As an example, FIG. 6 is a simplified diagram illustratingSOD delimiter being used in data frame.

In a PON system, the distances between subscribed ONUs and the OLT aredifferent, and hence the optical signal power loss and channel penaltiesvary with different ONUs. For example, power levels for signals aredifferent when they arrive at the OLT. Therefore, it is usually arequirement for the OLT to automatically adjust the received power leveland synchronize the received signal correctly with its clock reference.Usually, these functions are performed by the AGC and CDR module in theOLT.

At the OLT side, the Boundary Detector includes a SOD Correlator. Amongother things, the SOD Correlator is used for delineating the data frameboundary of the upstream signal from the ONU. For example, as shown inFIG. 3, the SOD delimiter is not protected by the FEC code, and the biterror probability is relatively high. The SOD Correlator is required totolerate bit errors since the transmitted SOD delimiter at the receiverside is often very likely be corrupted by bit errors. For example, thenumber of bit errors can be tolerated by the SOD Correlator is definedby a predetermined synchronization threshold. Often the synchronizationthreshold in the SOD Correlator is decided according to the operatingbit error level.

By setting up a suitable synchronization threshold, the SOD Correlatorof OLT can effectively delineate the received signal quickly andminimize the mean time of false lock occurrence. Typically, conventionalsystems set the synchronization threshold of the SOD Correlator at 12.If the computed HD between the SOD delimiter and the 66 bits receiveddata is less than 12, then the OLT declares a successful synchronizationwith the received signal. On the other hand, if the HD is equal orlarger than 12 then the received signal is shifted by one bit and theSOD Correlator re-calculates the HD between the SOD delimiter and thenew 66 bits data until a successful synchronization is declared.

There are various problems with the conventional approach discussedabove. Among other things, since the SOD delimiter is not protected bythe FEC code, the bit error probability of the SOD delimiter over thetransmission channel is often high. As a result, it requires the SODdelimiter to have a large HD between the SOD delimiter and the FSC. Forexample, conventional SOD delimiter and the FSC have a minimum HD equalto 31.

However, the theoretical suggested minimum HD between a SOD delimiterand FSC can be calculated using Equation 1 below:

$\begin{matrix}{{{{{Minimum}\mspace{14mu}{Hamming}\mspace{14mu}{Distance}} = {\lfloor \frac{N - 1}{2} \rfloor = {\lfloor \frac{66 - 1}{2} \rfloor = 32}}},{N\mspace{14mu}{is}\mspace{14mu}{length}\mspace{14mu}{of}\mspace{14mu}{SOD}}}\mspace{371mu}} & {{Equation}\mspace{14mu} 1}\end{matrix}$

The theoretical suggested value of the maximum synchronizationthreshold, so that the performance of SOD Correlator can be calculatedusing Equation 2 below:

$\begin{matrix}{{{Delineation}\mspace{14mu}{Threshold}\mspace{20mu} T} = {{\lfloor \frac{N}{4} \rfloor - 1} = {{16 - 1} = 15}}} & {{Equation}\mspace{14mu} 2}\end{matrix}$

It is to be appreciated that an objective of the present invention is toprovide a set of Start of Data <SOD> delimiters in which they complywith the theoretical suggested value. For example, the minimum HDbetween the SOD delimiter and the FSC is 32.

In a specific embodiment, the present invention provides a SODcorrelation circuit based on the using of one or more SOD delimiters.Among other things, the embodiment provides a fast synchronizationalgorithm for various synchronization thresholds.

Depending on the application, various SOD delimiters may be used. As anexample, Table 1 below illustrates five exemplary SOD delimiters:

TABLE 1 Minimum SOD HD between Allowable Max length SOD Delimiter(hexadecimal SOD Synchronization (bits) numbers) and FSC Threshold 66 116 A2 DC 69 F0 CD EE 40 32 15 66 1 5A E3 94 B6 66 C7 E0 03 32 15 66 1 7FA0 96 0E 14 A7 33 66 32 15 66 1 70 3A 08 6D ED 4E 99 66 32 15 66 0 41 BDB2 B3 D5 A7 C8 F0 32 15

The SOD delimiters as shown in Table 1 comply with the theoreticalsuggested minimum HD between a SOD delimiter and FSC. Among otherthings, the SOD delimiters have sixteen “0”s and seventeen “1”s on the33 even positions and on the 33 odd positions, or vice versa. As aconsequence, the SOD have a number of “0” not equal to the number of“1”, (e.g., either 32 “0”s plus 34 “1”s or 34 “0” s plus 32 “1”s). As anexample, all the SOD delimiters, in their binary forms, all conform tothe described requirement. For example, the following SOD delimiters areshown in hexadecimal numbers and their binary forms have 34 “0”s and 32“1”s,

0x 1 16 A2 DC 69 F0 CD EE 40

01 00010110 10100010 11011100 01101001 11110000 11001101 1110111001000000

0x 1 5A E3 94 B6 66 C7 E0 03

01 01011010 11100011 10010100 10110110 01100110 11000111 1110000000000011

0x 1 7F AO 96 0E 14 A7 33 66

01 01111111 10100000 10010110 00001110 00010100 10100111 0011001101100110

0x 1 70 3A 08 6D ED 4E 99 66

01 01110000 00111010 00001000 01101101 11101101 01001110 1001100101100110

The following delimiter has 32 “0”s and 34 “1”s,

0x 041 BD B2 B3 D5 A7 C8 F0

00 01000001 10111101 10110010 10110011 11010101 10100111 1100100011110000

The SOD delimiters shown in Table 1 comply with the theoreticalsuggested minimum HD between the SOD delimiter and the FSC. For example,these SOD delimiters, as well as other SOD delimiters contemplated bythe present invention, can be used to replace conventional SOD delimiterso that the minimum HD can be increased from 31 to 32 without additionalcomplexity or modifying the existing data frame structure. In otherwords, the present invention can decrease the false locking probabilitywithout any extra cost.

In an embodiment, a SOD delimiter complies with the theoreticalsuggested value of the minimum HD between a SOD delimiter and FSC. TheSOD delimiter must have sixteen “0”s and seventeen “1”s on the 33 evenpositions and on the 33 odd positions, or vice versa. Consequently, thenumber of “0”s must not be equal to the number of “1”s, (e.g., 32 “0”splus 34 “1”s, or 34 “0”s plus 32 “1”s).

To implement the embodiment, the binary form of the Hexadecimal sequenceis a 66 bits long sequence. For example, the binary form of {0x 1 16 A2DC 69 F0 CD EE 40} is {01 00010110 10100010 11011100 01101001 1111000011001101 11101110 01000000}. It should be noted that every hexadecimalnumber represent 4 binary bits, except the first hexadecimal number orthe leading number, which represents 2 binary bits.

FIG. 7 is a simplified diagram illustrating an upstream data framestructure of a 10G EPON system according to an embodiment of the presentinvention. This diagram is merely an example, which should not limit thescope of the claims in any way. One of ordinary skill in the art wouldrecognize many variations, alternatives, and modifications. As shown inFIG. 7, the SOD delimiters as listed in Table 1 are used in the dataframes.

It is to be appreciated that embodiments of the present invention have awide range of applicability and can be used in any systems that use SODdelimiters for synchronization with the received signal or fordelineating the boundary of data frame. In a specific embodiment, theinvention is to be used in a 10G EPON system based on IEEE 802.3standards.

At the ONU transmitter side, the SOD delimiter is appended to thebeginning of the FEC coded data frame as well as the HFP. For example,the HFP is used as a preamble for the transmitted upstream signal.

At the OLT receiver side, the SOD Correlator calculates the HD betweenthe received signal and the SOD delimiter to test if the HD is less thanthe system's synchronization threshold. In contrast to conventionalsystems, the synchronization threshold is adjustable according to therequirement of the system. For example, the false locking probabilitycan be minimized if T is set to be 0.

FIG. 8A is a simplified diagram illustrating a synchronization circuitof the SOD Correlator according to an embodiment of the presentinvention. This diagram is merely an example, which should not limit thescope of the claims in any way. One of ordinary skill in the art wouldrecognize many variations, alternatives, and modifications. As shown inFIG. 8A, a shifter register is used to process the receive ONU packetsand provide the processed packets to the Hamming distance calculation(HDC) module. The Hamming distance calculation module determines thedelineation based on the Hamming distance calculation.

FIG. 8B is a simplified diagram illustrating hard logic for providingSOD delimiter logic according to an embodiment, of the presentinvention. This diagram is merely an example, which should not limit thescope of the claims in any way. One of ordinary skill in the art wouldrecognize many variations, alternatives, and modifications. As shown,the SOD delimiter for this particular situation is “0x 1 16 A2 DC 69 F0CD EE 40”.

As long as the OLT detects an upstream signal from the ONU, itsynchronizes its clock reference with the upstream signal. The OLT thensends the received data into the Shift Register of the SOD Correlator.Once the Shift Register has been filled with 66 bits received data, itpasses these 66 bits through an electrical circuit that is based on theSOD delimiter. The electrical circuit is defined as the following: everybit of the SOD delimiter responds to a direct electric logic form theShift Register to HDC module. If the bit of the corresponding bit of theSOD delimiter is “0”, then the originally received data bit is sent tothe HDC module unchanged. On the other hand, if the corresponding bit ofthe SOD is “1”, then it passes the binary complement value of thereceived data bit to the HDC module (i.e., “0” changed to “1” or “1”changed to “0”). The HDC module calculates the corresponding HD andpasses the output to the Synchronization Decision Module (SDM). Finally,the SDM determines if it is a valid synchronization or not. If asuccessful synchronization is declared, then the OLT knows the beginningof the data frame and starts to receive data.

In an embodiment, the present invention provides a fast synchronizationalgorithm on the binary format of the HD from the SDM. The algorithm isimplemented with the 66-bits SOD delimiter. The minimum HD between theSOD delimiter and all possible 66 bits binary sequence is 0. The maximumHD between the SOD delimiter and all possible 66 bits binary sequence is66. Since 2⁶<66<2⁷, it requires at least 7 binary bits to represent theresulted HD in a binary format.

According to Table 2, the SDM can count on the number of consecutive “0”bits from the Most Significant Bit (MSB) to Least Significant Bit (LSB)to determine whether it is a valid synchronization or not, if thesynchronization threshold T is to be set as T=8=2³ or T=16=2⁴. Forexample, if T=8, then the SDM just need to check if the first 4consecutive bits are 0 or not.

TABLE 2 Hamming HD binary format Distance (MSB)  (LSB) 0 0 0 0 0 0 0 0 10 0 0 0 0 0 1 2 0 0 0 0 0 1 0 3 0 0 0 0 0 1 1 4 0 0 0 0 1 0 0 5 0 0 0 01 0 1 6 0 0 0 0 1 1 0 7 0 0 0 0 1 1 1 8 0 0 0 1 0 0 0 9 0 0 0 1 0 0 1 100 0 0 1 0 1 0 11 0 0 0 1 0 1 1 12 0 0 0 1 1 0 0 13 0 0 0 1 1 0 1 14 0 00 1 1 1 0 15 0 0 0 1 1 1 1 16 0 0 1 0 0 0 0

Assuming the number of bits required to represent the binary form of HDis n, and the synchronization threshold is set to be T=2^(m), where0≦m≦n. Then the SDM can decide if it is a valid synchronization bychecking whether the first n-m consecutive bits are 0's or not. If theyare all 0, then SDM can declare a successful synchronization. Otherwisethe Shift Register will shift one bit to obtain a “new” 66 bits data tobe tested with the SOD delimiter.

It is to be appreciated that various embodiments of the presentinvention provide numerous advantages over conventional techniques.Among other thing, the data frame implemented using an SOD delimiteraccording to the present invention can decrease the false lockingprobability. At the same time, this implementation does not introduceany complexity overhead.

FIG. 9 is a graph illustrating the comparison of false lockingprobability between existing techniques and an embodiment of the presentinvention. As an example, the length of the HFP is 4000 bits. From thegraph in FIG. 9, it can be seen that the false locking probability ismuch lower in the embodiment of the present invention. The dotted linesrepresent the Threshold T=12 and the dash lines represent the ThresholdT=15.

In addition to better performance, embodiments of the present inventionalso provide more flexibility when compared to conventional systems. Forexample, synchronization Threshold T is adjustable according to thesystem requirement. Fast synchronization algorithms can be adopted fordifferent threshold values.

Among other things, embodiments of the present invention provide fiveStart of Data <SOD> delimiters. Each of the SOD delimiter is ideallysuited for Ethernet PON upstream transmission.

In embodiments, the HFP can have binary form as “10101010 10101010 . . .”, which ends with a “0.” The HFP can still provide the AGC and CDRfunctions. In the embodiments, the hexadecimal number of the SOD is {0xC D5 8A 60 A4 E1 43 BC 9D} and its binary sequence is {11 1010101101010001 00000110 00100101 10000111 11000010 00111101 10111001}. Theminimum distance of the current employed SOD delimiter and the FSC is31.

If the binary sequence “10101010 10101010 . . . ”, which ends with a “0”is used as the HFP in the system, the SOD delimiters, which comply withthe HD between the SOD delimiters and FSC, are in the complement form ofSOD delimiters provided in Table 1. The corresponding SOD delimiters areshown in Table 3.

TABLE 3 Minimum SOD HD between Allowable Max length SOD Delimiter(hexadecimal SOD Synchronization (bits) numbers) and FSC Threshold 66 497 BA C4 69 F0 4C 88 FD 32 15 66 4 A5 38 D6 92 99 1C F8 3F 32 15 66 4 01FA 96 8F D7 1A 33 99 32 15 66 4 F1 A3 EF 49 48 8D 66 99 32 15 66 C 7D 42B2 32 54 1A EC F0 32 15

The SOD delimiters as shown in Table 3 comply with the theoreticalsuggested minimum HD between a SOD delimiter and FSC. Among otherthings, the SOD delimiters have sixteen “1”s and seventeen “0”s on the33 even positions and on the 33 odd positions, or vice versa. As aconsequence, the SOD have a number of “0” not equal to the number of“1”, (e.g., either 32 “0”s plus 34 “1”s or 34 “0” s plus 32 “1”s). As anexample, all the SOD delimiters, in their binary forms, all conform tothe described requirement. For example, the following SOD delimiters areshown in hexadecimal numbers and their binary forms have 34 “0”s and 32“1”s,

0x 4 97 BA C4 69 F0 4C 88 FD

10 11101001 01011101 00100011 10010110 00001111 00110010 0001000110111111

0x 4 A5 38 D6 92 99 1C F8 3F

10 10100101 00011100 01101011 01001001 10011001 00111000 0001111111111100

0x 4 01 FA 96 8F D7 1A 33 99

10 10000000 01011111 01101001 11110001 11101011 01011000 1100110010011001

0x 4 F1 A3 EF 49 48 8D 66 99

10 10001111 11000101 11110111 10010010 00010010 10110001 0110011010011001

The following delimiter has 32 “1”s and 34 “0”,

0x C 7D 42 B2 32 54 1A EC F0

11 10111110 01000010 01001101 01001100 00101010 01011000 0011011100001111

The LSB of binary bits and field (8 bits per field) positions is on theleft. Hexadecimal numbers are shown in a normal hexadecimal form and twohexadecimal numbers represent one corresponding field. For example, thefield “0x BA” (shown in Table 3) is sent as 01011101, representing 11thto 18th bits of the 66 bits SOD delimiter 1. The LSB for each field isplaced in the lowest number position of the field and is the firsttransmitted bit of the field. It is noted that a hexadecimal numberrepresents 4 binary bits, except the first hexadecimal number or theleading number, which represents 2 MSBs of corresponding four binarybits representation. For example, the binary representation of “0x 4” is“0010” and the first hexadecimal number “0x 4” represents 10.

FIG. 10 is a simplified diagram illustrating an upstream data framestructure of a 10G EPON system according to an embodiment of the presentinvention. This diagram is merely an example, which should not limit thescope of the claims in any way. One of ordinary skill in the art wouldrecognize many variations, alternatives, and modifications. As shown inFIG. 7, the SOD delimiters as listed in Table 3 are used in the dataframes.

In embodiments, the HFP can be a sequence of n consecutive specific66-bit blocks, in which the 66-bit block has a binary form as “10 11111101 0000 0010 0001 1000 1010 0111 1010 0011 1001 0010 1101 1101 10011010”, where the hexadecimal representation is {0x 4 BF 40 18 E5 C5 49BB 59}. The HFP is suitable for high speed PON systems (e.g.10G-EPONsystem) not only good for the AGC and CDR functions but also suitablefor applying Peak Detector or Equalizer at the receiver side of an OLT.In the embodiments, the hexadecimal number of the SOD is {0x 8 6B F8 D812 D8 58 E4 AB} and its binary sequence is {01 1101 0110 0001 1111 00011011 0100 1000 0001 1011 0001 1010 0010 0111 1101 0101}. The minimumHamming distance of the current employed SOD delimiter and the FSC is30.

If the above HFP is used in the system, the SOD delimiters that have alarge HD between the SOD delimiters and FSC are shown in Table 4.

TABLE 4 Minimum SOD HD between Allowable Max length SOD Delimiter(hexadecimal SOD Synchronization (bits) numbers) and FSC Threshold 66 86B F8 D8 12 D8 58 E4 AB 30 14

The SOD delimiters have fourteen “1”s and nineteen “0”s on the 33 evenpositions and on the 33 odd positions, or vice versa. As a consequence,the SOD have a number of “0” equal to the number of “1”, (e.g., either33 “0”s plus 33 “1”s). As an example, all the SOD delimiters, in theirbinary forms, all conform to the described requirement. For example, thefollowing SOD delimiters are shown in hexadecimal numbers and theirbinary forms have 33

“0”s and 33 “1”s,

0x 8 6B F8 D8 12 D8 58 E4 AB 01 11010110 00011111 00011011 0100100000011011 00011010 00100111 11010101.

The LSB of binary bits and field (8 bits per field) positions is on theleft. Hexadecimal numbers are shown in a normal hexadecimal form and twohexadecimal numbers represent one corresponding field. For example, thefield “0x BA” (shown in Table 3) is sent as 01011101, representing 11thto 18th bits of the 66 bits SOD delimiter 1. The LSB for each field isplaced in the lowest number position of the field and is the firsttransmitted bit of the field. It is noted that a hexadecimal numberrepresents 4 binary bits, except the first hexadecimal number or theleading number, which represents 2 MSBs of corresponding four binarybits representation. For example, the binary representation of “0x 4” is“0010” and the first hexadecimal number “0x 4” represents 10.

Although specific embodiments of the present invention have beendescribed, it will be understood by those of skill in the art that thereare other embodiments that are equivalent to the described embodiments.Accordingly, it is to be understood that the invention is not to belimited by the specific illustrated embodiments, but only by the scopeof the appended claims.

In embodiments, the HFP can be a sequence of n consecutive specific66-bit blocks, in which the 66-bit block has a binary form as “10 01111101 0110 0000 1010 1001 1111 0101 1000 0010 1010 0111 1101 0110 00001010”, where the hexadecimal representation is {0x 4 BE 06 95 AF 41 E56B 50}. The HFP is suitable for high speed PON systems (e.g.10G-EPONsystem) not only good for the AGC and CDR functions but also suitablefor applying Peak Detector or Equalizer at the receiver side of an OLT.In the embodiments, the hexadecimal number of the SOD is {0x 4 BE E4 B1DA AA 13 18 B1} and its binary sequence is {10 0111 1101 0010 0111 10001101 0101 1011 0101 0101 1100 1000 0001 1000 1000 1101}. The minimumdistance of the current employed SOD delimiter and the FSC is 31.

If the above HFP is used in the system, the SOD delimiters that have alarge HD between the SOD delimiters and FSC are shown in Table 5.

TABLE 5 Minimum SOD HD between Allowable Max length SOD Delimiter(hexadecimal SOD and Synchronization (bits) numbers) FSC Threshold 66 4BE E4 B1 DA AA 13 18 B1 31 15 66 4 BE A4 03 50 32 BF 3A E3 31 15 66 C AE85 47 BE 2B 06 24 A7 31 15 66 4 FE 82 16 48 79 BA 98 B3 31 15

The SOD delimiters have fourteen “1”s and nineteen “0”s on the 33 evenpositions and on the 33 odd positions, or vice versa. And the number of“0” and “1” on the odd bit and even bit constitutes a cross combination;if on the odd bit, there are 14 “0”, and 19 “1”, then on the even bit,there would be 19 “0” and 14 “1”. As a consequence, the SOD have anumber of “0” equal to the number of “1”, (e.g., either 33 “0”s plus 33“1”s). As an example, all the SOD delimiters, in their binary forms, allconform to the described requirement. For example, the following SODdelimiters are shown in hexadecimal numbers and their binary forms have33

“0”s and 33 “1”s,

0x 4 BE E4 B1 DA AA 13 18 B1

10 01111101 00100111 10001101 01011011 01010101 11001000 0001100010001101

0x 4 BE A4 03 50 32 BF 3A E3

10 01111101 00100101 11000000 00001010 01001100 11111101 0101110011000111

0x C AE 85 47 BE 2B 06 24 A7

11 01110101 10100001 11100010 01111101 11010100 01100000 0010010011100101

0x 4 FE 82 16 48 79 BA 98 B3

10 01111111 01000001 01101000 00010010 10011110 01011101 0001100111001101

The LSB of binary bits and field (8 bits per field) positions is on theleft. Hexadecimal numbers are shown in a normal hexadecimal form and twohexadecimal numbers represent one corresponding field. For example, thefield “0x BA” (shown in Table 3) is sent as 01011101, representing 11thto 18th bits of the 66 bits SOD delimiter 1. The LSB for each field isplaced in the lowest number position of the field and is the firsttransmitted bit of the field. It is noted that a hexadecimal numberrepresents 4 binary bits, except the first hexadecimal number or theleading number, which represents 2 MSBs of corresponding four binarybits representation. For example, the binary representation of “0x 4” is“0010” and the first hexadecimal number “0x 4” represents 10.

Although specific embodiments of the present invention have beendescribed, it will be understood by those of skill in the art that thereare other embodiments that are equivalent to the described embodiments.Accordingly, it is to be understood that the invention is not to belimited by the specific illustrated embodiments, but only by the scopeof the appended claims.

What is claimed is:
 1. A method of providing upstream datasynchronization in an optical communication network, comprising: sendingdata from an optical network unit, wherein the data comprises a firstdata frame and the first data frame comprises a header sequence, asynchronization segment, and a data segment, wherein the synchronizationsegment comprises 66 bits and the 66 bits comprise a first number ofbits having nonzero values and a second number of bits having values ofzero, wherein the header sequence comprises a sequence and the sequencein binary form comprises 10 1111 1101 0000 0010 0001 1000 1010 0111 10100011 1001 0010 1101 1101 1001 1010, and wherein the synchronizationsegment comprises another sequence and the another sequence in binaryform comprises 01 1101 0110 0001 1111 0001 1011 0100 1000 0001 1011 00011010 0010 0111 1101
 0101. 2. The method of claim 1, further comprisingreceiving the first data frame by an optical line terminal andprocessing the first data frame.
 3. The method of claim 1, furthercomprising determining a Hamming distance and a boundary of the firstdata frame.
 4. The method of claim 3, further comprising decoding thefirst data frame based on the boundary.
 5. The method of claim 3,wherein the Hamming distance has a minimum value of
 32. 6. The method ofclaim 3, wherein determining the Hamming distance comprises calculatinga distance between the first segment and a synchronization delimiter. 7.A method of receiving data in an optical communication network,comprising: receiving data from an optical network unit, wherein thedata comprises a first data frame and the first data frame comprises aheader sequence, a synchronization segment, and a data segment, whereinthe synchronization segment comprises 66 bits and the 66 bits comprise afirst number of bits having nonzero values and a second number of bitshaving values of zero, wherein the header sequence comprises a sequenceand the sequence in binary form comprises 10 1111 1101 0000 0010 00011000 1010 0111 1010 0011 1001 0010 1101 1101 1001 1010, and wherein thesynchronization segment comprises another sequence and the anothersequence in binary form comprises 01 1101 0110 0001 1111 0001 1011 01001000 0001 1011 0001 1010 0010 0111 1101
 0101. 8. The method of claim 7,further comprising receiving the first data frame by an optical lineterminal and processing the first data frame.
 9. The method of claim 7,further comprising determining a Hamming distance and a boundary of thefirst data frame.
 10. The method of claim 9, further comprising decodingthe first data frame based on the boundary.
 11. The method of claim 9,wherein the Hamming distance has a minimum value of
 32. 12. The methodof claim 9, wherein determining the Hamming distance comprisescalculating a distance between the first segment and a synchronizationdelimiter.
 13. An Optical Network Unit (ONU) in a Passive OpticalNetwork system, comprising: a transmitter, wherein the ONU is configuredto send data using the transmitter, wherein the data comprises a firstdata frame and the first data frame comprises a header sequence, asynchronization segment, and a data segment, wherein the synchronizationsegment comprises 66 bits and the 66 bits comprise a first number ofbits having nonzero values and a second number of bits having values ofzero, wherein the header sequence comprises a sequence and the sequencein binary form comprises 10 1111 1101 0000 0010 0001 1000 1010 0111 10100011 1001 0010 1101 1101 1001 1010, and wherein the synchronizationsegment comprises another sequence and the another sequence in binaryform comprises 01 1101 0110 0001 1111 0001 1011 0100 1000 0001 1011 00011010 0010 0111 1101
 0101. 14. The ONU of claim 13, wherein the ONU isfurther configured to receive the first data frame by an optical lineterminal and process the first data frame.
 15. The ONU of claim 13,wherein the ONU is further configured to determine a Hamming distanceand a boundary of the first data frame.
 16. The ONU of claim 15, whereinthe ONU is further configured to decode the first data frame based onthe boundary.
 17. The ONU of claim 15, wherein the Hamming distance hasa minimum value of
 32. 18. The ONU of claim 15, wherein the ONU isconfigured to determine the Hamming distance by calculating a distancebetween the first segment and a synchronization delimiter.
 19. A PassiveOptical Network system, the system comprising: an optical network unitthat is configured to send data using a transmitter, wherein the datacomprises a first data frame and the first data frame comprises a headersequence, a synchronization segment, and a data segment, wherein thesynchronization segment comprises 66 bits and the 66 bits comprise afirst number of bits having nonzero values and a second number of bitshaving values of zero, wherein the header sequence comprises a sequenceand the sequence in binary form comprises 10 1111 1101 0000 0010 00011000 1010 0111 1010 0011 1001 0010 1101 1101 1001 1010, wherein thesynchronization segment comprises another sequence and the anothersequence in binary form comprises 01 1101 0110 0001 1111 0001 1011 01001000 0001 1011 0001 1010 0010 0111 1101 0101; and an optical lineterminal comprising: a receiver configured to receive at least the firstdata frame; a shifter register configured to store the first data frame;a logic circuit configured to compare the first segment with asynchronization delimiter; a Hamming distance module configured todetermine a Hamming distance based on the first segment; and adelineation decision module configured to determine a boundary of thefirst data frame.
 20. The Passive Optical Network system of claim 19,wherein the Hamming distance module is configured to determine theHamming distance by calculating a distance between the first segment andthe synchronization delimiter.